Apparatus for installing and maintaining subaquatic petrol tanks

ABSTRACT

A service installation for underwater servicing operations including a service unit, a working bell supported by the service unit, a control chamber carried by the bell and separable therefrom by a watertight door, a submerged base, the bell being movable on to the base to there form with the base a watertight chamber and a transfer chamber coupled to the service unit and movable to the bell when the latter is on the base and connectable to the control chamber for transfer of a work crew via the control chamber to the bell.

Le Therisien Dec. 24, 1974 APPARATUS FOR INSTALLING AND MAINTAINING SUBAQUATIC PETROL TANKS [75] Inventor:

Louis G. Le Therisien, Paris, France Assignee: Subsea Equipment Associates Limited (Seal), Hamilton, Bermuda Filed: June 28, 1972 Appl. No.: 266,920

[30] Foreign Application Priority Data June 28, 1971 France 71.23429 US. Cl. 61/69, 166/.5 Int. Cl E2lb 7/12 Field of Search 166/.5, .6; 61/69; 175/27,

References Cited UNITED STATES PATENTS 8/1967 Paull et al 166/.5 X ll/1967 Blanding et a1 166/5 3,408,822 11/1968 Chate et al. 166/.5 X 3,421,579 1/1969 Manning 166/.5

3,512,583 5/1970 James 166/.5 3,650,323 3/1972 Kan-ady 166/.5 3,656,549 4/1972 Holbert c1 a1 (51/69 X 3,714,995 2/1973 Hancs et a1, .1 175/27 Primary Examiner-Frank L. Abbott Assistant ExaminerRichard E. Favrcau Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT 15 Claims, 6 Drawing Figures PATENTED DEC 2 4 I974 sumsur gs i I. LI II II. II III:- t a a mm 3 a sum 5 o APPARATUS FOR WSTALLING AND MAINTAINING SUBAQUATIC PETROL TANKS The invention refers to a system for underwater servicing operations and particularly undersea oilwell heads and the maintenance of these wellheads inside an enclosure enabling men to work in an atmosphere of which the composition and the pressure are compatible with work by men.

Various systems have already been proposed to enable working on an undersea oilwell head placed in an enclosure subjected to atmospheric pressure but none of them appear to present the characteristics necessary to a maintenance operation of long duration whilst ensuring complete safety of the work crews.

Bells are well known which are specially arranged for establishing a watertight joint with a base and for lowering a work crew in a watertight compartment in the interior of the latter, but bells of this kind only offer limited safety, particularly in the event of leaks from the wellhead and the creation of an-explosive atmosphere after placing of the bell and evacuation of the water which it contains.

Furthermore, the bells of this kind have, by reason of their positive buoyancy, a cable attaching the bell in a permanent manner to the undersea base, so that the bell is a dependent both of the base and the intervention unitto which it is joined by supporting cable and by energy supply cable.

On the other hand apparatus are known which cap the wellhead and extend to the surface of the water so as to enable direct access to the wellhead, but these apparatus cannot serve wellheads in deep water and they still exhibit the safety defects previously indicated.

More refined systems consist in surrounding the wellhead with a fixed capsule in order to isolate the wellhead permanently from the marine medium and in providing maintenance of the capsule by a service chamber which travels to and is coupled with the capsule.

Although these latter systems display the advantage of being able to serve one or possibly several wellheads by means of a single service chamber, they do not, by reason of their conception, enable perfect safety to be ensured, asthe service chamber must couple itself directly to a capsule of which the functioning may be faulty and of which the atmosphereean be vitiated or liable to cause an explosion. Furthermore, the capsule having to exhibit a volume sufficient to make maintenance possible, the cost of such systems is high, the more so that a capsule is necessary for each wellhead in an extended oilfield.

According to the present invention there is provided an installation for underwater operations such as wellhead servicing characterised in that it comprises a base on the bottom, a workbell provided with a control and operation chamber fast with and externally of the bell and separated from it a watertight door for separating the control chamber and the bell, an external watertight door for closing the control chamber, a guide structure on the base to guide the bell relative to the latter, the bell being positionable on the base to constitute therewith a watertight envelope, a mother unit above the base, and a means of connection between the bell and the mother unit for lowering and raising the bell, a work crew transfer chamber having a ballast tank to regulate buoyancy, guide and propulsion means and an exit door giving access to an open trunk for engaging around the external door of the control and operation chamber in order to fonn with that chamber a watertight compartment.

Such a system presents a series of supplementary advantages contributing to the end in view. In the first place it is sufficient merely to equip each undersea well in a zone under exploitation with a simple base in order to service each wellhead of the group from a single mother unit, using a single workbell and a single transfer chamber. ln the second place, the transfer chamber being separated from the workbell by the operation and control chamber, integral with the bell but external to the latter, it can be seen that the safety of the personnel is considerably increased since in the event of unhealthy conditions in the workbell, it becomes possible for the personnel to retreat into the trunk of reduced dimensions which constitutes the control chamber and from there to regenerate the air before returning to the transfer chamber.

The system defined above may include a removable connection by pipe between the mother unit and the bell.

In this way it becomes easy to take advantage of the mother unit for preparing the watertight joint between the bell and the base by injecting air under pressure into the pipe soas to expel the water rapidly from the bell when it arrives in the vicinity of the base. It is then sufficient, once the bottom of the bell is emptied of water and is placed on the base, to place the end of the pipe in the mother unit in communication with the atmosphere in order to cause the bottom of the bell to bed on the base.

Furthermore, withdrawal of the connecting pipe when the bell is applied to the base in a watertight manner by reason of the difference in pressure between the outer medium and the inner medium facilitates manoeuvering of the transfer chamber with it is piloted to the control chamber. Likewise, risk is avoided of tangling the connecting pipe with an umbilical cable joining the transfer chamber to the mother unit. If the mother unit is a boat, the connection of the bell to the boat is subjected to the action of a device for compensating for vertical movement of the boat. Withdrawal of the connection releases the device for other operations.

A watertight connection is provided between the base of the system and the casing joined to the wellhead by making use of a connection joining together mechanically and in a watertight manner the different concentric casing members constituting the wellhead.

For safety of the personnel, the workbell may be provided with noxious gas detector apparatus, means in the control chamber responsive to the detector for filling the bell with water, and means for introducing into the bell a sufficient quantity of nitrogen so that after withdrawal of the water the nitrogen is at atmospheric pressure.

It then only requires operators provided with individual respiratory equipment to descend into the bell again in order to carry out the required work there, the same operation being repeatable if the safety conditions were no longer satisfied.

Safety conditions being thus always assured, it can be seen that it is possible to perform easily and at any depth any work carried out at the surface, whether it is a matter of placing simple or complex wellheads orparatus, for example, or connections of the receiving network and electric cables.

Other objects and characteristics of the invention will be evident from the following description of a preferred embodiment thereof, given by way of example, reference being made to the accompanying drawings wherein:

FIG. 1 is a schematic representation of the whole of the system;

FIG. 2 is a schematic plan view of an alternative embodiment the base of the system;

FIG. 3 is a section along the line III-III in FIG. 2;

FIGS. 4a and 4b, meeting along the line a-a, are a schematic representation partially in section of the upper and lower portions of the transfer chamber and the workbell after joining together in the embodiment of FIG. 1, and

FIG. 5 is a schematic view partially in section of the connector from the base to the casing and lining in the embodiment of FIG. 1.

After completion of a drilling l, a horizontal base is I installed composed essentially of the base 2 (FIGS. 1, 4b, and 5) or 200 (FIGS. 2 and 3) to which is welded a reinforcement and guide structure 3 and a connector 80 fixing the base in a rigid and-watertight manner to the casing head 4 closed by the cap 83. The reinforcement and guide structure 3 contacts the submarine surface on the underside of the ring 3a.

A workbell 5 is hung on an air carrier pipe 6 provided with any suitable type of electronic device 28a for positioning the axis of the bell relative to the axis of the well, for lowering from a mother unit, here a boat 7, on to the base 2. Bearer means, indicated schematically at 8, serve for transporting and handling heavy loads such as that represented at 9.

A work crew transfer chamber 10 is hung on a cable 11 from a hoist means 12, of any kind suitable for lowering to a level in the vicinity of that of the workbell 5. Locating and/or guide means as well as propulsive means 14 enable convenient joining of the end of a a trunk 15 on chamber 10 to a control and operating chamber 13 provided with an outside door 16.

After joining of the chambers 10 and 13, personnel may pass from the former into a lock chamber formed by the trunk 15 and chamber 13 and then into the control chamber 13 which is on the outside of the bell and separable from the latter by a watertight door 17. Safety means, which will be explained in greater detail during the description of the chamber 13, enable effective and permanent control of the condition of the medium prevailing in the bell 5 once emptied of water and including changing the medium or regenerating it. A

work crew can, given correct conditions in the bell,

open the door 17 and pass into the bell 5 to carry out the work to be done, a crew member being posted in the control chamber 13 to supervise the various control and operation apparatus with a view to ensuring perfect safety of the work crew.

Thus the basic members of the system for working at atmospheric pressure on each wellhead of a group and under conditions of perfect safety are: a substantially horizontal base for each wellhead, a single workbell capable of defining with each base a water-tight enclosure, a control and operation chamber externally of the bell and separable from it by a watertight door, a single transfer chamber capable of effecting a junction with the operation chamber, and a single mother unit servv ing the said bell.

Although each of the members of this system can appear in the most diverse forms and comprise, in addition to the means indispensable to effecting the combination which has just been defined, auxiliary means in variable number for facilitating the performance of the functions of the members of the system, a preferred embodiment of each of these members will be described by way of example. It will be noted in particular that the mother unit can be either a floating unit or a grounded unit, and may be on the surface, submerged or semi-submerged. The unit includes in addition means of locating the means of connection of the bell relative to the base.

The base 2 or 200 consists of a steel structure of which the thicknesses are selected to resist fully the difference in pressure existing between the outside medium at the level of the well and atmospheric pressure, the bell being in addition loaded to the maximum and being able to contain, for example, an equipment of some tens of tons to be installed on the well.

This structure can be produced in a number of ways, the two structures shown in the drawings being only preferred embodiments of the invention. The structure shown in FIGS. 1, 4b, and 5 comprises simply a large flat base 2 mounted on top of the guide and reinforcement structure 3. The structure shown in FIGS. 2 and 3 comprises an annular crown 2', a skirt 18 welded underneath the crown 2', and a thick slab l9 welded to the skirt 18. In the FIGS. 2 and 3 embodiment. the guide and reinforcement structure 3 is connected to the crown 2 at its lower part. The upper surface of the base 2 serves as a bearing face for a joint 33 on the workbell 5 as shown in FIG. 4b. The upper surface of the crown 2' serves a similar function, but the joint 33 is not shown in FIG. 3. In the centre of the slab 19 in the FIGS. 2 and 3 embodiment is an orifice 21 for admitting the connector 80. Similarly, in the centre of the base 2 in the FIGS. 1, 4b, and 5 embodiment is an orifice 21' for admitting the connector 80. In both cases, the connection of the connector 80 to the member through which it protrudes is watertight, but the connection is illustrated in detail only in FIG. 5. In that figure, the base 2 is show bolted to the flange 85a of the connector 80 by means of the bolts 22. seen in FIG. 3, the skirt 18 may be bored with orifices 20 servi admit and secure gathering network pipes and electric cables 2. Naturally the orifices 20 are made watertight around the elements 92 to prevent seawater from passing therethrough and Welling upwardly into the workbell 5 through the central opening in the annular crown 2'.

The connector 80, more easily seen in FIG. 5, comprises essentially the body proper surrounding the casings of greatest diameter 81 and 82 and being fitted by any sort of sealing means to the casing head 4, the latter being capable of being joined to any known wellhead member, for example, the cap 83. In accordance with the invention, the body 85 bears on the upper end of the casings 81 and 82 through the shoulder 85b and on the upper end of the casing 82 through the crown 850. In addition a blocking mechanism represented schematically at 84 integrates the inner wall of the, body 85 with the outer wall of the casing 81. Other members, joints, locks, unlocking controls, etc., can be fitted to the connector 80, but these members, being indispensable neither to the understanding of the invention nor to the functioning of the system, have not been shown and will not be described.

The crown 21 2 is bored again at 23, FIG. 3, to admit four guide posts 24 integral with a stand 25, FIGS. 2 and 3, which has served for the drilling. A flexible structure 26, FIG. 3, attached to the crown 2', is surmounted at its upper portion by a section of a coneshaped guide plate 27 providing guidance of the workbell during its placing on the base 200. Thus even if the bell offers itself with a misalignment of some tens of centimetres, it is suitably guided, first by the section of the guide plate 27, then by the structure 26 up to the placing of the bell. Furthermore the flexibility of the whole enables a major portion of the shock to be absorbed at the moment of engagement of the bell with the guide structure. The wellhead is protected from the direct effects of chains, cables, anchor lines, etc., by the structure 26.

The mother unit being, in the example chosen, the boat 7, the latter includes a handling equipment 28,

FIG. 1, for lowering, raising and putting the workbell 5 in place. This equipment is provided with an antiroll device and a device to compensate for rise and fall of the boat. A control point 29 is provided for operation of this equipment as well as the supply of electric power to the system. It also serves to control a high-capacity, high-pressure air-compressor 30 enabling compressed air at the pressure obtaining at the level of the well to be sent through the pipe 6. It can also control the valve 31 in a workbell 5 isolating the latter from the pipe 6, a means of operation being in addition provided for closing the valve 31 systematically during the withdrawal of the pipe 6 which, in accordance with a characteristic of the invention, is preferably detachable. The valve 31 may be of any suitable type, and, as many such valves are already well known to the art, both of a type which are remotely controllable and of the type which respond automatically to preselected conditions, it is shown only schematically.

The workbell depicted at-S, FIG. 4b, rests on the base 2 by means of a part 32 bearing the joint 33. In accordance with a preferred embodiment of the invention, the part 32 is removable in order to enable, on the one hand, its possible replacement in the event of modificationand, on the other hand, its replacement by a part of greater height with a view to placing on the wellhead equipments of larger dimensions. The closed space formed by the application of the bell workbell 5 to the base 2 is designed to give sufficient room to give a crew access all round production equipment 34 transported in the bell 5 for erection on the wellhead. The bearer means 8 in the bell enable the equipment 34 to be positioned and to be lowered from a suspended position 34' to a final position. The bearer means 8 can be conventional devices with hooks, pulley blocks, jacks, etc., none of them have been shown on the drawing of FIG. 4b for greater clarity.

The control and operating chamber 13, FIG. 4a and 4b, separable from the body of the workbell 5 by the door 17 is accessible from the outside through a door 16 mounted on a bearing surface on which bears the edge of the skirt which is extended by a guide and protective skirt 35. An annular guide 36 brings about perfect alignment of the lower edge of the skirt 15 on the chamber 13.

As the various apparatus comprising the equipment of the control chamber can be of any kind, these apparatuses have been depicted on the drawing in a purely symbolic manner. A unit 37 containing a pump delivering, for example, 6 to 10 m /hour ata pressure of the order of 50 bars and over, is provided for discharging water from the workbell 5 via a circuit 38. A hydraulic unit 37a coupled to an operation panel 39 enables the operator to operate a winch 40 via circuits 41 and to operatein addition a certain number of jacks via circuits 42.

Bottles of air, oxygen and nitrogen represented at 43 in FIG. 4b are connected to circuits 44 for producing the required atmosphere in the workbell 5. An air conditioner 45 contains regeneration cartridges, a heating system and a blower serving circuits 46. An electrical switchboard 48 controls the pump, the air conditioner 45, and telemetering apparatus 50 via connections 49, 51, and 52. Connections 53 serve all the other circuits: lighting, transformers, telephone, television.

The current supply, although it can be direct from the mother unit, is preferably by way of the transfer chamber 10. Rapid coupling and uncoupling connection boxes 54in a circuit 55 of the transfer chamber 10 connect the electrical circuits of the switchboard 48 in the control chamber 13 to the power source.

Other rapid coupling and uncoupling connection boxes 56 couple distribution circuits 57, the respiratory mixture coming from a distributor 58 joined by circuits 59 to bottles 60 to feed respiratory mixture to the control chamber 13.

The transfer chamber is closed by two doors 61 and 62, the first to resist the internal pressure, the second to resist the external pressure. An auxiliary door, not shown, enables rapid evacuation.

A ballast tank 63 is provided to regulate buoyancy of the transfer chamber 10, and with propellers 14 assists in making an easy and precise approach of the chamber 10 over the chamber 13, then the descent for applying the lower edge of the skirt 15 to the horizontal upper edge of the chamber 13. A pump 64, having an electri cal control circuit 65, will empty the lock chamber which the skirt 15 forms with the upper part of the chamber 13. The control of this operation is carried out after opening valves 66 ad 67 in pipework 68 coupling the pump to the lock chamber. Resilient bumpers 90 are provided to protect the transfer chamber 10.

In order not to overload the drawing uselessly, showing of the whole of the circuits which enable both the operation of the ballast tank 63 and the propellers 14 (which can function independently of one another, both forwards and in reverse so as to be able especially to rotate the chamber 10 about itself), has been avoided. In the same way, the various electrical circuits and especially those enabling the installation of cameras in the workbell 5, in the lock chamber and the other chambers with the object of transmission to the mother unit, have not been shown.

Obviously in addition to portholes arranged especially in the doors 16 and 17 and in the walls of the transfer chamber 10, various remote guidance apparatus, for example, sonar, are provided to facilitate the approach operations with a view to joining up.

It will be understood that the transfer chamber 10 can include a number of auxiliary or necessary equipments such, for example, as a rescue winch 69 operated either manually or hydraulically via a circuit 70. A

manual control 71 of a valve 72 is likewise shown, for discharging air initially in the skirt 15. Finally the transfer chamber 10 can include, besides the external members such as the bottles 60 and the pump 64, handling apparatus of known type, for example, tongs for cleaning a base during the maintenance of a wellhead, as will be described.

Prior to applying the bell to a well and after checking all the equipments including dumpable ballast, auxiliary batteries and the whole of the connections intended to join the workbell to the transfer chamber. the transfer chamber 10 is lowered by cable 11 fastening it to the mother unit. To do this the doors 61 and 62 are closed, the valve 72 opened and ballast tank 63 filled so as to give the transfer chamber 10 a negative buoyancy. Having reached the proximity of the well, the operator modifies the weight of the ballast to give the transfer chamber 10 a substantially zero buoyancy in order to facilitate its displacement in answer to the guidance apparatus such as sonars, then to manoeuvring apparatus following on direct observation by the operator through sighting apparatus or television camera, for example, projectors facilitating inspection of the well. It is thereby possible to discover if the workbell can be set down. Where necessary the base 2 or 200 is cleared both outside and inside the guide structure 26 27, FIG. 3. This operation is carried out by means of tongs operated by hydraulic circuits joined to the hydraulic unit 370.

Return of the transfer chamber 10 to the surface is carried out by controlling its buoyancy and bringing the latter to a strongly negative buoyancy at the moment when the bell arrives in the vicinity of the surface, in order to reduce the ball effects.

Lowering of the workbell 5 is carried out after opening valve 31 establishing communication between the interior of the bell 5 and atmosphere via the rigid pipe 6. The support devices and the devices for centering the bell on the mother unit are of any kind and have not been depicted. These devices are used in combination with the means for locating the well and the workbell guidance means including the positioning device 28a to align the well axis and the bell axis to a toleranceof say tens of centimetres.

On approach to the well or whenever necessary, the

device on the mother unit for compensating for rise and fall of the mother unit is operated to avoid collision of the workbell 5 and the guide plate 27 and the base 2. When the workbell is above the well and its edges are some metres from the base 2, the water is evacuated from the workbell 5 by passing compressed air down the pipe 6 which may be a drill string. The compressor 30 of the installation can deliver, for example, 30 m /hour at 50 bars. Displacement of the water by air is checked by measuring the air feed, by watching for bubbles rising to the surface and by use of television cameras. When the workbell is resting on the base 2, a valve 91 at the surface is progressively opened to put the pipe 6 in communication with the atmosphere in order to bring about sealing of the joint at the edge of the workbell 5 against the base 2. During this period, the rise and fall compensating device is in service. Then again, as the pressure of the water applies a considerable force on the joint 33 and the removable part 32 of the workbell 5, the latter remains fixed against the base 2 limiting in that way the movement of the upper end of the pipe 6. Means not shown enable on the one hand reduction of the displacements of the mother unit relative to the pipe 6 and on the other hand absorption of part of the horizontal forces by a connection of a certain flexibility.

The workbell 5 being thus set in place and at atmospheric pressure, the valve 31 is automatically closed and withdrawal of the pipe 6 proceeds. This latter operation avoids any risk of collision between the transfer chamber 10 and the pipe 6 during manoeuvring the former to place it on the bearing surface of the control and operation chamber 13 used for the linking up, as well as the necessity of keeping the rise and fall compensating device in action. When the transfer chamber has been positioned with the assistance of the propellers l4 and means of guidance and sighting, an operator operates the pump 64 and empties the interior of the skirt 15 forming with the closed door 16 of the control chamber 13 the lock chamber. The valve 72 is previously closed by operation of the manual control 71 and the valve 67 is opened. After discharge of the water, bringing about the watertight joint at the edges of the skirt 15 against the outer part of the control chamber 13, the operator opens the doors 61 and 62 after having reestablished the balance of pressure between the transfer chamber 10 and the interior of the lock chamber by a pipe, not shown, provided with valves in the two enclosures.

The work crew proceeds'with joining up connections such as 54 and 56 joining the respiratory mixtures distribution circuits of the transfer chamber 10 and the control chamber 13 as well as the various electrical, telephonic and television circuits. Balance of pressure between the control chamber 13 and the lock chamber is brought about by means like those existing for balancing the pressures between the lock transfer chamber and the chamber 10.

The work crew open the door 16 and go into the control chamber 13 from which they can check by means of telemetering indicators 50 that the amounts of CO 0 and H 8 are within the required limits. In the event of suitable conditions being detected, one of the operators remains in the operation and control chamber 13 while the other operators go down into the bell after opening the door 17. This operation is carried out after balancing of the pressures by means like those used to restore the balance between the transfer chamber 10 and the lock chamber.

[f the working conditions analysed in the control chamber 13 do not or no longer correspond with the required safety conditions, the crew remain in the control chamber 13, the door 17 is closed or kept closed, and refilling of the workbell 5 with water proceeds. This refilling can be effected by utilizing part of the circuit 38 after having closed the valve 73, FIG. 4a, and after having opened the valves 74 and 75. Exhausting of the gas can be effected if necessary through the pipe 76 after opening the valve 77.

After complete filling of the workbell 5 with water, the valves 77 and are reclosed and a certain volume of nitrogen is introduced by means of one of the circuits operated by the valve 78 of circuit 44, this volume being sufficient to fill the whole bell at atmospheric pressure when the water has been completely pumped out by means of the pump contained in the unit 37 after opening of the valves 73 and 74, the valve 75 remaining closed. The pumping operation restores the watertight joint between the edges of the workbell 5 and the base 2, this seal being obtainable by reason of the heavy weight of the workbell.

Under the conditions now prevailing, the operators equip themselves with a self-contained breathing apparatus and re-enter the bell after having previously closed the manually operated valve 79. The latter can also be operated from the chamber 13, the wheel 79a symbolizing this control. The operators then proceed with the work assigned to them with the help of tools placed at their disposal and especially hydraulic manipulators fed by the circuits 42 terminating in jacks, winches, etc. previously provided. During this work one operator maintains contact between the control chamber and the mother unit and keeps watch over the maintenance of the safety conditions in the interior of the workbell with the assistance of the telemetering apparatus.

After the work has been carried out, the work crew reopens the valve 79 and refills the workbell with water after going into the control chamber 13 and closing the door 17. The atmosphere in the control chamber is then regenerated by absorption of H 8 and CO and then adding a sufficient quantity of oxygen. The effects of the pressure on the door 17 are limited by mechanical means of any kind. The operators can then take off their individual breathing apparatus and go through into the transfer chamber 10 from which they can control the introduction of water into the lock chamber by manipulation of the valve 72, for example. After the refilling, the transfer chamber-10 is brought back to the surface.

The bell is then raised on to the installation by the equipments of the mother unit, equipped with the rise and fall compensating device if it is a case of a boat.

Although the invention has been described with reference to a preferred embodiment of the system provided with a workbell, a control and operating chamber, a transfer chamber and a base of particular forms intended'to illustrate the invention, it will be understood that a number of modifications could be applied to the structures depicted without thereby departing from the present invention. .By way of example, the transfer chamber can be lowered and raised on the in' stallation utilizing the same means of handling as those utilized for the workbell and utilizing the same cable or on the contrary, as depicted in FIG. 1, utilizing a separate cable. Again the valve 31 can be both electrically operated from the mother unit at the surface and by a mechanism actuated by the withdrawal of the pipe 6 and conversely an electro-mechanical mechanism of any kind enabling, for example, withdrawal of the pipe 6 to be prevented while the valve remains open. It will be understood moreover, that work capable of being carried out in accordance with the system which is the objectof the invention can consist in attaching to the arrives at the required pressure. The means of operation of the dumpable ballasts can be of any kind, manual or automatic. Finally, the system could be utilized for any underwater installation necessitating the intervention of a work crew having to work under conditions similar to atmospheric conditions or not, but in complete safety.

I claim:

1. An apparatus for installing and maintaining equipment submerged in a body of water in cooperation with a service unit and a work crew transfer chamber, said apparatus comprising:

1. a generally horizontal base fixed permanently to the floor of said body of water;

2. a generally cup-shaped workbell resting removably on said horizontal base in a seal-tight manner, said workbell being open on the side thereof adjacent to said horizontal base so that said horizontal base and said workbell together define an interior space which is isolated from said body of water;

3. a control chamber mounted on said workbell and having:

a. a first water-tight door connecting said control chamber to said interior space; b. a second water-tight door adapted to connect said control chamber to the transfer chamber; c. means for allowing water to enter into said interior space;

d. means for pumping water from said interior space;

e. means for monitoring the composition of a gaseous atmosphere contained within said interior space; and

f. a first means for introducing a first gasinto said.

from the position in which it rests on said horizon- I I tal base.

2. Apparatus as claimed in claim 1:

1. wherein said workbell has a negative buoyancy when filled with air, whereby said workbell can be filled with air before it rests on said generally horizontal base, and

2. further comprising a cone-shaped guide structure open at the base thereof and fixedly connected to said generally horizontal base with the open base of said guide structure" remote from said generally horizontal base, whereby said guide structure. can be used to guide said workbell into position on said generally horizontal base without the use of guide cables.

3. Apparatus as claimed in claim 1 and further comprising means for positioning said workbell relative to said base.

4. Apparatus as claimed in claim 1 1. wherein said means for coupling the service unit to said workbell comprises aflexible conduit providing a passageway for air between said interior space and the service unit and 2. said apparatus further comprises a source of compressed air, located on the service unit and in interruptable communication with said flexible conduit,

whereby said source of compressed air can be used to drive water from said workbell when said workbell is in position above said base.

5. Apparatus as claimed in claim 1 wherein the portion of said generally cup-shaped workbell adjacent to said generally horizontal base is removable.

6. Apparatus as claimed in claim 1 wherein said generally horizontal base comprises 1. an upper slab, which slab is the portion of said base on which said workbell rests, and

2. a skirt supporting said upper slab and fixedly attached to the underside thereof, said skirt having a plurality of orifices therein for receiving and coupling piping.

7. Apparatus as claimed in claim 1 1. wherein the equipment is a well head and 2. said generally horizontal base is coupled to said well head in a sealing-tight manner by means of a connector having a body fixed sealingly to said base, said connector having an inner surface shaped to engage the outer surface of said well head in a sealing-tight fashion, thereby isolating a portion of said well head from said body of water, said portion being located in said interior space.

8. Apparatus as claimed in claim 1 and further comprising l. a second means for introducing a second gas into said interior space and 2. means for evacuating gas from said interior space,

whereby air contained in said interior space can be evacuated therefrom if said means for monitoring the composition of a gaseous atmosphere contained within said interior space indicate that said gas does not correspond with the required safety conditions, said workbell can be filled with water, nitrogen can then be introduced into said workbell, repair can be accomplished by a work crew working in the nitrogen atmosphere with the aid of selfcontained breathing apparatus, said workbell can then again be filled with water, and finally air can.

again be introduced into said workbell.

9. Apparatus as recited in claim 1 and further comprising means for regulating the pressure of gases introduced by said first and second means for introducing gas into said interior space, whereby said gases can be brought to a predetermined pressure in said workbell as water is pumped therefrom.

10. Apparatus as claimed in claim 1 wherein said control chamber further comprises first and second connections located exteriorly thereof, said first and second connectors being positioned for rapid connection to mating connectors located on the work crew transfer chamber, said first connector serving to permit electrical power to be introduced into said control chamber from the transfer chamber and said second connector serving to permit a respiratory mixture to be introduced into said control chamber from the transfer chamber.

11. Apparatus as claimed in claim 1 and further comprising a pipe connected to said workbell and providing a passageway for air between said interior space and the service unit, whereby air may be forced through said pipe from the service unit to said interior space.

12. Apparatus as claimed in claim 11 I. wherein said pipe is removably connected to said workbell and 2. further comprising:

a. a first valve located in said workbell where said pipe is connected thereto, said first valve being movable between a first position in which it permits communication between said pipe and said interior space and a second position in which it does not permit communication between said pipe and said interior space and b. means for ensuring that said pipe can only be disconnected from said workbell when said first valve is in its second position.

13. Apparatus as claimed in claim 11 1. wherein said pipe is removably connected to said workbell and 2. further comprising:

a. a first valve located in said workbell where said pipe is connected thereto, said first valve being movable between a first position in which it permits communication between said pipe and said interior space and a second position in which it does not pennit communication between said pipe and said interior space and b. means for automatically moving said first valve from its first position to its second position on the spheric air and a second position in which said interior space is not in communication with atmospheric air.

15. Apparatus as claimed in claim 14 wherein said second valve is located in a portion of said pipe located in the service unit.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,855,806 DATED December 24, 1974 INVENTOR(S) Louis G. Le Therisien It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE SPECIFICATION:

Col. 3, Lines 10 & ll, Delete of an alternative embodiment the base of the system;", and insert --of the base of an alternative embodiment of the system, the stand 25 being shown in the top half of the view only;--.

Col. 4, Line 45, after "is", delete "show", insert --shown--.

Line 46, before "seen", insert --As best-.

Line 47, delete "servi", insert -serving--.

Line 49, delete "2", insert --92--;

after "Naturally", insert Col. 5, Line 4, delete "21 2", insert --2'--.v

Line 31, before "valve" delete "the", insert --a--.

Line 32, before "workbell" delete "a", insert --the--.

Line 50, before "workbell" delete bell". I

Cpl. 7, Line 49, after "workbell", insert --5-.

C01. 8, Line 35, after "lock" delete "transfer".

Line 36, before "chamber 10'', insert --transfer.

Signed and Scaled this seventh Day of oereberrws [SEAL] A ttest:

RUTH C. M A ISON C. MARSHALL DANN Arresting Qffrcer Commissioner oflatenrs and Trademarks 

1. An apparatus for installing and maintaining equipment submerged in a body of water in cooperation with a service unit and a work crew transfer chamber, said apparatus comprising:
 1. a generally horizontal base fixed permanently to the floor of said body of water;
 2. a generally cup-shaped workbell resting removably on said horizontal base in a seal-tight manner, said workbell being open on the side thereof adjacent to said horizontal base so that said horizontal base and said workbell together define an interior space which is isolated from said body of water;
 3. a control chamber mounted on said workbell and having: a. a first water-tight door connecting said control chamber to said interior space; b. a second water-tight door adapted to connect said control chamber to the transfer chamber; c. means for allowing water to enter into said interior space; d. means for pumping water from said interior space; e. means for monitoring the composition of a gaseous atmosphere contained within said interior space; and f. a first means for introducing a first gas into said interior space, whereby a work crew can enter said control chamber either from the transfer chamber through said second water-tight door or from said interior space through said first watertight door, and can, while in said control chamber with said first watertight door closed, control the atmosphere in said interior space; and
 4. means for coupling the service unit to said workbell for lowering and raising said workbell to and from the position in which it rests on said horizontal base.
 2. a generally cup-shaped workbell resting removably on said horizontal base in a seal-tight manner, said workbell being open on the side thereof adjacent to said horizontal base so that said horizontal base and said workbell together define an interior space which is isolated from said body of water;
 2. Apparatus as claimed in claim 1:
 2. further comprising a cone-shaped guide structure open at the base thereof and fixedly connected to said generally horizontal base with the open base of said guide structure remote from said generally horizontal base, whereby said guide structure can be used to guide said workbell into position on said generally horizontal base without the use of guide cables.
 2. said generally horizontal base is coupled to said well head in a sealing-tight manner by means of a connector having a body fixed sealingly to said base, said connector having an inner surface shaped to engage the outer surface of said well head in a sealing-tight fashion, thereby isolating a portion of said well head from said body of water, said portion being located in said interior space.
 2. means for evacuating gas from said interior space, whereby air contained in said interior space can be evacuated therefrom if said means for monitoring the composition of a gaseous atmosphere contained within said interior space indicate that said gas does not correspond with the required safety conditions, said workbell can be filled with water, nitrogen can then be introduced into said workbell, repair can be accomplished by a work crew working in the nitrogen atmosphere with the aid of self-contained breathing apparatus, said workbell can then again be filled with water, and finally air can again be introduced into said workbell.
 2. further comprising: a. a first valve located in said workbell where said pipe is connected thereto, said first valve being movable between a first position in which it permits communication between said pipe and said interior space and a second position in which it does not permit communication between said pipe and said interior space and b. means for ensuring that said pipe can only be disconnected from said workbell when said first valve is in its second position.
 2. a skirt suPporting said upper slab and fixedly attached to the underside thereof, said skirt having a plurality of orifices therein for receiving and coupling piping.
 2. said apparatus further comprises a source of compressed air, located on the service unit and in interruptable communication with said flexible conduit, whereby said source of compressed air can be used to drive water from said workbell when said workbell is in position above said base.
 2. furtheR comprising a second valve located in said pipe and movable between a first position in which said interior space is in communication with atmospheric air and a second position in which said interior space is not in communication with atmospheric air.
 2. further comprising: a. a first valve located in said workbell where said pipe is connected thereto, said first valve being movable between a first position in which it permits communication between said pipe and said interior space and a second position in which it does not permit communication between said pipe and said interior space and b. means for automatically moving said first valve from its first position to its second position on the withdrawal or breakage of said pipe.
 3. Apparatus as claimed in claim 1 and further comprising means for positioning said workbell relative to said base.
 3. a control chamber mounted on said workbell and having: a. a first water-tight door connecting said control chamber to said interior space; b. a second water-tight door adapted to connect said control chamber to the transfer chamber; c. means for allowing water to enter into said interior space; d. means for pumping water from said interior space; e. means for monitoring the composition of a gaseous atmosphere contained within said interior space; and f. a first means for introducing a first gas into said interior space, whereby a work crew can enter said control chamber either from the transfer chamber through said second water-tight door or from said interior space through said first watertight door, and can, while in said control chamber with said first water-tight door closed, control the atmosphere in said interior space; and
 4. means for coupling the service unit to said workbell for lowering and raising said workbell to and from the position in which it rests on said horizontal base.
 4. Apparatus as claimed in claim 1
 5. Apparatus as claimed in claim 1 wherein the portion of said generally cup-shaped workbell adjacent to said generally horizontal base is removable.
 6. Apparatus as claimed in claim 1 wherein said generally horizontal base comprises
 7. Apparatus as claimed in claim 1
 8. Apparatus as claimed in claim 1 and further comprising
 9. Apparatus as recited in claim 1 and further comprising means for regulating the pressure of gases introduced by said first and second means for introducing gas into said interior space, whereby said gases can be brought to a predetermined pressure in said workbell as water is pumped therefrom.
 10. Apparatus as claimed in claim 1 wherein said control chamber further comprises first and second connections located exteriorly thereof, said first and second connectors being positioned for rapid connection to mating connectors located on the work crew transfer chamber, said first connector serving to permit electrical power to be introduced into said control chamber from the transfer chamber and said second connector serving to permit a respiratory mixture to be introduced into said control chamber from the transfer chamber.
 11. Apparatus as claimed in claim 1 and further comprising a pipe connected to said workbell and providing a passageway for air between said interior space and the service unit, whereby air may be forced through said pipe from the service unit to said interior space.
 12. Apparatus as claimed in claim 11
 13. Apparatus as claimed in claim 11
 14. Apparatus as claimed in claim 11
 15. Apparatus as claimed in claim 14 wherein said second valve is located in a portion of said pipe located in the service unit. 